This invention relates to compositions and methods for enhanced fixation of implants to bone.
Although acrylic bone cement (self-curing poly-methyl-methacrylate) (PMMA) has been the mainstay of total hip and knee fixation for over three decades, it is inert and does not form a bone bond. Rather, it induces the formation of a fibrous membrane, which separates the implant cement mantle from the approximating host bone. Accordingly, it has been recognized that PMMA merely forms a mechanical fixation, as opposed to a biological bond of tissue.
Despite many efforts to improve acrylic cement, the desired end result of increasing the longevity of implant fixation and decreasing aseptic loosening has, to date, not greatly changed the long-term prognosis of implant recipients treated with such cements.
In recent years, investigators have sought to move from xe2x80x9ccement fixationxe2x80x9d to xe2x80x9cbioactive fixationxe2x80x9d with bioactive materials such as hydroxyapatite, bioactive glasses or ceramics. Bioactive glass is a bioactive silica-structured glass that undergoes a corrosive chemical reaction of dissolution, leaching and precipitation when contacted with tissue (body) fluids, simulated body fluids (SBFs) or aqueous solutions which permit interaction of the bioactive glass with approximating cells and tissues. These chemical reactions promote the formation of a carbonate hydroxyapatite (HCA) layer upon the bioactive ceramic or glass core, which acts as an osseoconductive (bone forming stimulus) agent, and new bone formation bridges the gap between the implant and the adjacent host bone (osseointegration), thus forming a true biological bond. However, the disadvantage of
known bioactive glass or other bioactive ceramic systems, even when mixed with appropriate resins, is that it takes months to produce enough new bone to achieve weight-bearing capacity. This is in contrast to the quick-fix-set of PMMA cement which at least provides in immediate weight-bearing capacity, even though as noted above, tending to fail in the long term.
The present invention provides a solution to the problems with known cements by providing a composition comprising (a) microscopic anhydrous pellets or particles containing the most important components of biological fluids or synthetic biological fluids (SBFs), (b) bioactive glass or other bioactive ceramic particles and (c) an appropriate resin such as, but not limited to, bisphenol-alpha-glycidyl methacrylate (BIS-GMA), to form a bone-forming cement which enhances (accelerates) bone production and bone bonding.
As a recipient""s body or tissue fluids contact the components of the composition of this invention, a corrosive chemical reaction begins in which the anhydrous pellets or particles containing the components of biological fluids or SBF pellets are dissolved, thereby enhancing the corrosive chemical reaction at the surface of the bioactive glass or ceramic, and thereby accelerating a more uniform and significant amount of bone formation, not only on the surface of the cement mantle, but penetrating to a deeper level throughout the entire thickness of the mantle until the stem surface is reached. This process occurs in a continuous fashion over a period of time shorter than that typically required for bone infiltration when using bioactive glass or ceramic alone. The presence of anhydrous particles of biological fluids or SBFs, upon dissolution, produces voids into which bone cells easily migrate, until all the voids created by the dissolution of the pellets and the spaces between the resin particles are filled in with bone. This process is significantly different and superior to the quick initial cure and fixation set that occurs with PMMA cements, or the unacceptably long period of time required with bioactive glass or bioactive ceramic alone.
Accordingly, it is one object of this invention to provide a composition for rapidly and securely fixing an implant to a recipient""s bone, while at the same time promoting autogenous bone infiltration into the cementous mantle about the implant.
A further object of this invention is to provide a method for rapidly and securely fixing an implant to a recipient""s bone, while at the same time promoting autogenous bone infiltration into the cementous layer about the implant.
A further object of this invention is to provide a method for making and using a composition for rapidly and securely fixing an implant to a recipient""s bone, while at the same time promoting autogenous bone infiltration into the cementous layer about the implant.